docs: def step_rhythmic(self, tau=1.0, error_coupling=1.0):
          """Generate a single step of x for rhythmic 
          closed loop movements. Decaying from 1 to 0 
          according to dx = -ax*x.
          
          tau float: gain on execution time
                     increase tau to make the system execute faster
          error_coupling float: slow down if the error is > 1
          """
          self.x += (1 * error_coupling * tau) * self.dt
          return self.x